To fit a contact lens to a patient\'s eye, a keratometer can be used to measure
ID: 2122922 • Letter: T
Question
To fit a contact lens to a patient's eye, a keratometer can be used to measure the curvature of the cornea-the front surface of the eye. This instrument places an illuminated object of known size at a known distance p from the cornea, which then reflects some light from the object, forming an image of it. The magnification M of the image is measured by using a small viewing telescope that allows a comparison of the image formed by the cornea with a second calibrated image projected into the field of view by a prism arrangement. Determine the radius of curvature of the cornea when p =26 cm and M =0.0130.
Explanation / Answer
M = q/p
q = 0.013*26 =0.338 cm
f = pq/p+q =0.333 cm
R = 2f =0.667 cm